Device for adjusting position for cutting bags and packaging machine incorporating same

ABSTRACT

A form-fill-seal packaging machine produces a dummy bag from a film by starting to move seal jaws after the film has been pulled over a specified length or for a specified length of time from the moment when an eye mark on the film is detected by a detector. If the position on the film at which it was cut is displaced from the intended position, this displacement is inputted such that the specified length or the specified length of time is automatically corrected. If any of the parameters defining the pattern of transverse sealing operation is changed, the specified length or the specified length of time can also be automatically adjusted.

This is a divisional of application Ser. No. 09/505,020 filed Feb. 16,2000 now U.S. Pat. No. 6,403,599 which is now pending and is adivisional of application Ser. No. 09/306,481 filed May 6, 1999 U.S.Pat. No. 6,088,994 which is a continuation-in-part of application Ser.No. 09/233,768 filed Jan. 20, 1999, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a packaging machine of the so-calledform-fill-seal type adapted to concurrently form a bag from a film, tofill it with articles and to seal it to obtain individual packagedproducts. More particularly, this invention relates to a device foradjusting the position on the film at which it is cut (“cut-position”)to produce separated bags. The invention also relates to a packagingmachine adapted to automatically adjust the cut-position according to aninputted size of the bags to be produced.

Packaging machines adapted to concurrently bend a film into a tubularform, to fill it with articles to be packaged and to clamp it between apair of sealing members (“seal jaws”) to simultaneously seal the toppart of a filled bag and the bottom of the next bag to be filled havebeen known. If the bags are formed from a film with a design printedthereon corresponding to each bag to be formed, marks (hereinafterreferred to as the “eye marks”) which are detectable by a light sensorare printed on the film at longitudinal intervals corresponding to thelength of the bags to be made such that the film can be accuratelysealed over and cut at boundary areas between portions of the filmcorresponding to two mutually adjacent bags as the packaging machine isoperated to repeat a cyclic motion.

Prior art methods of determining the cut-position of the bags or theclamping position by seal jaws can be roughly divided into those ofadjusting the interval between the time when an eye mark on the film asa reference is detected and the time at which the film is cut (such asadjusting the dislocation of the cut-position while changing the timeset on a timer by operating a dial) and those of displacing the positionof the sensor for the eye marks (that is, to move the eye mark sensor bya distance corresponding to the displacement of the cut-position). Themethods of the former kind are not desirable because repeated trials anderrors tend to increase the wasted amount of the film. The methods ofthe latter kind are advantageous in that one has only to displace theeye mark sensor but it is a cumbersome operation to make the positionadjustment while watching the markings of a dial.

In the case of packaging machines of a continuously operated type havinga linearly moving transverse sealing mechanism, in particular, thecut-position of the film also changes whenever the stripping distance ischanged according to the kind of the articles to be packaged or thepattern of motion (such as the time of sealing) for the transverse sealjaws. Thus, the operator had to adjust the cut-position whenever such achange had to be made. This also contributed to increase the waste ofthe film material.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide an improveddevice for automatically adjusting the cut-position of a bag-making filmmaterial in response simply to an input of a displacement of thecut-position obtained from a dummy bag formed for testing.

It is also an object of this invention to provide a packaging machineincorporating such a device or method.

It is another object of this invention to provide a packaging machinecapable of cutting the film automatically at intended positions inresponse only to an input of the bag size or the eye mark position.

It is a further object of this invention to provide a device for apackaging machine for automatically adjusting the cut-position of abag-making film merely by transporting the film until a cut-position onthe film reaches the film-cutting position.

According to a method embodying this invention, the motion of a pair ofseal jaws is started after the film has been pulled over a specifiedlength or for a specified length of time (both referred to as “thetravel condition”) from the moment when an eye mark on the film isdetected by a detector to thereby obtain a dummy bag for examiningwhether the film was cut at a right position. If not, the displacementfrom the intended cut-position is measured and used to correct theinitially specified travel condition. Alternatively, the correction ofthe initially specified travel condition may be effected on the basis ofdisplacement of the clamping position due to changes in variousparameters for determining the pattern of the motion of the seal jaws.

A device embodying this invention may be characterized as comprising amemory for storing the aforementioned travel condition such as thedistance by which the film is initially caused to travel between thetime when an eye mark on the film is detected and the time when themotion of the seal jaws is to be started, an input means through whichthe displacement of the position on the film where it is actually cutand the intended cut-position is inputted, and calculating means foradjusting the aforementioned travel condition according to thedisplacement inputted through the input means.

A packaging machine of this invention may be characterized as comprisingfilm transporting means such as pull-down belts for moving a film alonga specified path, a detector for detecting an eye mark on the film, atransverse sealer operating cyclically and having a pair of seal jawsfor clamping the film from opposite sides and cutting it to form a bag,a memory for storing certain data such as desired length of the bags tobe made, and means for using these data to calculate a distance or timeof travel by the film and controlling the motion of the seal jaws andhence the timing of clamping the film thereby.

Since the initial motion of the film (expressed either by the distanceor time of its travel) is corrected by preliminarily producing a dummybag as a test and measuring the displacement of the actually cutposition from where the cutting was intended, the film-cutting positioncan be automatically and easily adjusted without wasting a large amountof film.

According to another method embodying this invention, the distance oftravel by the film is measured from the moment when an eye mark isdetected until the cut-position fixed on the film reaches the specifiedclamping position of the seal jaws and the timing of motion for the sealjaws at their initial positions is determined on the basis of thismeasured distance of travel. Accordingly, an adjusting device employingthis method of adjustment may be characterized as comprising means formeasuring and storing the distance of travel by the film from thedetection of an eye mark until the cut-position reaches the clampingposition and means for calculating the timing for starting the motion ofseal jaws at their initial positions. With such a method or a device,the film can be cut exactly at the intended cut-position and hence thewaste of the film can be reduced to a minimum merely by measuring thedistance of travel of the film from the detection of an eye mark untilthe cut-position reaches the clamping position of the seal jaws.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a schematic diagonal view of a part of a form-fill-sealpackaging machine incorporating a device for cutting bags according tothis invention;

FIG. 2 is a schematic block diagram of a control system for thepackaging machine of FIG. 1;

FIG. 3 is a block diagram of a control circuit which may be used in thecontrol system shown in FIG. 2;

FIG. 4 is a flow chart for the operation of the packaging machine ofFIG. 1 with control system shown in FIGS. 2 and 3;

FIG. 5 is a diagram for showing a pattern of the motion of a seal jaw;

FIG. 6 is a plan view of a portion of the film used in this invention;

FIG. 7 is another view of a portion of the film for explaining a methodembodying this invention;

FIG. 8 is a time chart for the operation of packaging machine accordingto a method of this invention;

FIG. 9 is a schematic block diagram of another control circuit which maybe used in the control system shown in FIG. 2; and

FIGS. 10A and 10B are flow charts for the operation of the packagingmachine of FIG. 1 with control system shown in FIGS. 2 and 9.

Some of like or equivalent components in different control circuits maybe indicated by the same symbols for convenience and may not beexplained repetitively.

DETAILED DESCRIPTION OF THE INVENTION

For the purpose of reference, there is schematically shown in FIG. 1 aform-fill-seal packaging machine of the so-called vertical pillow typewhich may incorporate the present invention. For convenience, FIG. 1shows only relevant parts of such a machine related to its forming,filling and sealing operations. U.S. Pat. No. 5,279,098 issued Jan. 18,1994, for example, may be referenced for a detailed account of generalstructure and operations of such a machine. FIG. 2 shows schematically acontrol system including a computer 20 broadly described here only ashaving a data storing means (“memory” 21) and means for performingvarious operations (“operating means” 22), which may be used for such apackaging machine. A control system according to one particularembodiment of the invention is described next with reference to FIG. 3showing its control circuit 10 more in detail. FIGS. 1, 2 and 3 will bereferenced next to explain this embodiment of the invention generally.

As shown in FIG. 1, an elongated web of flexible thermoplastic material(herein referred to as “the film”) 100 unwinds from a supply roll 90,being pulled by a pair of pull-down belts 81, and is guided by aplurality of guide rolls 91 towards a former 98 which serves to bend thefilm 100 into a tubular form. The pull-down belts 81 are operated by abelt-driving motor 83. A pulse generator 84 is attached to the driveshaft of this belt-driving motor 83, and the output pulse from thispulse generator 84 is adapted to be received by a film motion counter11.

After the mutually overlapping side edges of the tubularly formed film100 is thermally sealed together by a longitudinal sealer 82 as the film100 is pulled vertically downward along a specified film path, thetubular film 100 is sealed transversely (or horizontally) by atransverse sealer 50 Which is disposed below the pull-down belts 81 andincludes a pair of seal jaws 51. The pair of seal jaws 51 of thetransverse sealer 50 is disposed on mutually opposite sides of the filmpath and is adapted to move on generally D-shaped trajectories inmutually opposite directions so as to clamp the film 100 therebetween.Each of the seal jaws 51 is rotatably supported at one end of anelongated member (referred to as “the arm”) 52 adapted to rotate aroundan axis 59 at its other end such that both seal jaws 51 are alwaysoriented in the same direction as they rotate around the axes 59 (forexample, by means of a Schmidt coupling as illustrated in aforementionedU.S. Pat. No. 5,279,098).

The arms 52 are rotated by means of a servo motor (referred to as “thearm-rotating motor”) 53, and their axes 59 are adapted to be movedhorizontally towards each other or away from each other by means ofanother servo motor (referred to as “the axis-shifting motor”) 55.Control units for these servo motors 53 and 55 are indicated by numerals54 and 56, respectively. The control circuit 10 serves to control therotary motion of the arms 52 and the distance between their axes ofrotation 59 such that the seal jaws 51 undergo a rotary motion of aprescribed pattern on generally D-shaped trajectories in mutuallyopposite directions.

A shutter plate 57, biased horizontally by a spring, is attached to theupper surface of each seal jaw 51, and a stripping plate 58, similarlybiased horizontally by a spring, is attached to the bottom surface ofeach seal jaw 51. After the tubular film 100 is transversely sealed toform the bottom of a bag, articles to be packaged are dropped from ahopper 96 above the former 98. Both the shutter plates 57 and thestripping plates 58 are adapted to approach the film 100, immediatelybefore the seal jaws 51 engage each other in the next cycle to close thetop of the bag, such that the film 100 will be stripped while articlesbelatedly dropping down from above are prevented from entering the bagbeing about to be clamped and sealed transversely. Although not shown, ablade is provided on one of the seal jaws 51 for cutting the film 100horizontally across its sealed area immediately after the seal jaws 51engage each other, thereby separating the bag which has just been filledas a finished product. The sealed area serves also as the bottom edge ofthe next bag to be filled with articles.

Next, an example of the method of adjusting the position of cutting thefilm 100 for separating a finished bag will be outlined. First, thepull-down belts 81 are started such that the film 100 begins to travelalong its path, as described above. After one of the eye marks (notshown), provided at equal intervals on the film 100 as reference points,is detected by an eye mark sensor 95, the film 100 is caused by thecomputer 10 to advance by a provisionally specified distance before themotion of the seal jaws 51 from their provisionally specified initialpositions 510 is started. The eye mark sensor 95 may be of a typeserving to detect the eye marks by reflection or transmission of light.A detection signal therefrom is inputted to the control circuit 10 andserves as a starting time for synchronizing the motion of the film 100and the cyclic motion of the seal jaws 51. When the seal jaws 51 areengaged together at their specified clamping position 511 and the film100 is thereby cut by the blade to produce a dummy bag, the operation ofthe packaging machine is stopped and the dummy bag thus produced isexamined to see whether or not the film 100 was cut at the desiredcut-position. If the film 100 was cut at a position not exactlycoinciding with the intended cut-position, the displacement, or thedistance between these two points, is measured. The provisionally setdistance is changed by this distance.

The pattern of the motion (including the shape of the trajectories) ofthe seal jaws 51 is determined by many action parameters such as thestripping time (during which stripping is carried out prior to theclosing of a bag) and the sealing time (during which a filled bag istransversely sealed). If the user wishes to change any of these actionparameters, the position at which the seal jaws 51 come to engage eachother, for example, can be easily determined by a calculation from knownrelationships. Thus, the cut-position can be adjusted also by varyingthe aforementioned provisionally specified distance.

As shown schematically in FIG. 3, the distance traveled by the film 100is calculated by the film motion counter 11 from the number of rotationsof the belt-driving motor 83, or the pulses from the pulse generator 84as described above, and is received therefrom by a matching means 13 tobe described below. A distance, which is intended to be traveled by thefilm 100 from the moment when the eye mark sensor 95 detects one of theeye marks on the film 100 until the motion of the sealjaws 51 from theirinitial positions 510, is inputted initially as an initial condition (interms of number of pulses) through an input means 40 and is stored in amemory 12. The aforementioned matching means 13 is for outputting astart signal to the control unit 54 for the arm-rotating motor 53 tostart the rotary motion of the seal jaws 51 from their initial positions510 when the counted pulse number transmitted from the film motioncounter 11 matches the pulse number inputted through the input means 40and stored in the memory 12, as explained above. The angle of rotationby the arms 52 around the axes 59 as the seal jaws 51 move from-theirinitial positions 510 to the clamping position 511 is measured by apulse counter 14 by the rotation of the arm-rotating motor 53. Theaforementioned distance of displacement obtained by measuring on thetest bag is inputted by the user also through the input means 40, isconverted into a corresponding pulse number by a calculating means 16,and is outputted to an adjusting means 17 for adjusting the initiallyset distance value stored in the memory 12 by adding or subtracting thisdistance of displacement.

The input means 40 may be used also to input various action parametersfor the operation of the packaging machine as described above. The inputmeans 40 may comprise a touch screen, adapted to selectably displaydifferent images for specifying the size of the bags to be produced andthe kind of articles to be packaged. It may be adapted to allow thenumber N of cycles of operation (or the number of bags to be producedper unit time), the stripping distance, the length L_(b) of the bags tobe produced and the distance L_(C) between an eye mark and a positionfor cutting the film 100 to be inputted corresponding to the kind ofbags to be produced.

The angular velocity of the seal jaws 51 and their angular positionswhen they engage each other, calculated by the calculating means 16, arereceived by a parameter adjusting means 19 which serves to correct thecorresponding data already stored in a pattern memory 15 by adding orsubtracting corresponding correction values. A control signal isoutputted from this pattern memory to the control unit 85 for thebelt-driving motor 83 and also to the control unit 56 of theaxis-shifting motor 55 to move the axes 59 of rotation of the arms 52horizontally such that the seal jaws 51 will travel on trajectories ofa-desired shape as indicated in part by broken lines in FIG. 2.

FIGS. 4 and 5 are referenced next to explain the operations for theadjustment of the film-cutting position more in detail. The adjustmentis started by starting the belt-driving motor 83 while the seal jaws 51are stopped at their initial positions 510 and the film 100 begins tomove along its path (Step S1). When the eye mark sensor 95 detects aneye mark on the film 100 (YES in Step S2), a detection signal istransmitted to the film motion counter 11 to start measuring thedistance of travel by the film 100 thereafter by the number of pulses(Step 3).

A distance value by which the film 100 is to move during the wait timeperiod from the moment when an eye mark on the film 100 is detected bythe eye mark sensor 95 until the seal jaws 51 are to begin their rotarymotion is initially stored in the memory 12 as a number of pulses andthis pulse number is inputted to the matching means 13. When the pulsenumber representing the actual distance of travel of the film 100received from the film motion counter 11 reaches the pulse number storedin the memory 12 (YES in Step 4), the matching means 13 outputs a matchsignal, and the control unit 54 for the arm-rotating motor 53, inresponse to this match signal, causes the seal jaws 51 to start theirrotary motion from their initial positions 510 (Step S5). The angle oftheir rotary motion is monitored similarly by the number of pulses bythe pulse counter 14.

The trajectory of each seal jaw 51 is determined according to actionparameters stored in the pattern memory 15. As shown in FIG. 5, the sealjaw trajectory may be divided into an accelerating part W_(a) where theseal jaw 51 accelerates from the initial position 510, a preparatorypart W_(b) where the seal jaw 51 is accelerated or decelerated to beprepared for the following stripping action, a stripping part W_(c)where the stripping takes place and the seal jaw 51 moves on a straightline at a constant speed twice as fast as the film speed at which thefilm 100 is caused to travel downward, a sealing part W_(d) where thefilm 100 remains clamped while being transversely sealed and the sealjaws travel at the same speed as the film 100, a transition part W_(e)where the seal jaw 51 is accelerated or decelerated to change its speedand a return part W_(f) where the seal jaw 51 returns to the initialposition 510 at a constant speed. It now goes without saying that theaforementioned clamping position 511 at which the pair of seal jaws 51comes to be engaged with each other will shift if the distance D₁ foreffecting stripping and/or the time for sealing (while the seal jaws 51move a distance indicated by D₂ in FIG. 5) is changed.

When the seal jaws 51 reach the sealing position 511 (YES in Step S6) atthe end of the stripping part W_(c), the film 100 is transversely sealedwhile it travels on the sealing part W_(d) of the trajectory.

The motion of the seal jaws 51 as described above is effected accordingto the action parameter stored in the pattern memory 15 as describedabove. After a dummy bag is thus formed, the motors 83, 53 and 55 arestopped (Step S8) after a specified overrun period during which the film100 and the seal jaws 51 are allowed to move a certain extra distancebefore stopping (Step S7). The dummy bag thus formed is removed from themachine and examined to check if the film 100 was cut at the rightcut-position (Step S9).

If the user decides that there is a displacement requiring a correction(YES in Step S9), the distance by which the correction is to be made isinputted through the input means 40 to the calculating means 16 to beconverted into units of pulses and is added to or subtracted from theprovisionally set distance (in units of pulses) traveled by the film 100between the times when the eye mark is detected and when the motion ofthe seal jaws 51 is started (Step S10).

If the stripping distance D₁ is changed, depending on the kind of thearticles to be packaged, or if the sealing time is changed, depending onthe kind of the film 100 being used or the speed of packaging, such thatthe action parameters of the operation are changed (YES in Step S11),the angular velocity of the seal jaws 51 between the initial position510 and the clamping position 511, as well as the clamping position 511itself will change. Thus, the action parameters of the arm-rotatingmotor 53 and the axis-shifting motor 55 are appropriately changedaccordingly (Step S12).

Next, FIG. 2 is referenced to describe another aspect of the inventionwherein the input means 40 is used to input not only the number N ofcycles of operation, the stripping distance, the length L_(b) of eachbag and the distance L_(C) between an eye mark and a position forcutting the film 100 for each of various kinds of articles to bepackaged, but also parameters common to all kinds of bags to beproduced, such as the distance L between where an eye mark is detectedby the sensor 95 and the clamping position 511 of the seal jaws 51.Although the distance L can theoretically be calculated by the operatingmeans 22 of the computer 20 from the design specifications of thepackaging machine, there are always some deviations from thespecification and, when a film is actually loaded and the machine isoperated, there may be detected a finite displacement. If thisdisplacement is measured and the distance L is corrected by using thismeasured displacement value, a more precise operation of the machinebecomes possible. The method for this correction is described below.

Examples of data stored in the memory 21 of the computer 20 include N,L_(b) and L_(C), as defined above, for each kind of articles to bepackaged. The distance L between where an eye mark is detected and wherethe film is clamped (the clamping position 511) is also stored. If theuser specifies a kind of articles to be packaged through the input means40, the corresponding data N, L_(b) and L_(C) are retrieved from thememory 21 and may be displayed on a screen (not shown) which may be apart of the input means 40.

On the basis of these retrieved data, the operating means 22 calculatesvarious control parameters for the seal jaws 51 and the pull-down belts81, transmitting them to the control units 54, 56 and 85 therefor.Examples of these control parameters include the initial position 510 ofthe seal jaws 51, their angular velocities in various parts W_(a)-W_(f)of their trajectory as they undergo a cyclic motion and the distancebetween the axes 59 in each of these trajectory parts W_(a)-W_(f). Theseparameters are calculated according to the selected bag size and thespeed of operation.

The initial position 510 is determined such that the seal jaw 51starting to move therefrom and the cut-position on the film 100 beingtransported will come together at the clamping position 511 at the sametime. Let T denote the time required for the seal jaw 51 to reach theclamping position after starting to move from the initial position 510when an eye mark is detected. Since this is also the time during which acut-position on the film 100 must reach the clamping position 511, thefollowing condition must be satisfied

X=TV=L−nL _(b) +L _(C)

(as shown in FIG. 6 wherein eye marks and cut-positions on the film 100are indicated by numerals 101 and 102, respectively) where L is asdefined above, X is the distance traveled by the film 100 in this timeinterval T, V is the constant speed at which the film 100 is pulled bythe pull-down belts 81, and n is an integer representing the number ofbags to be made from the portion of the film 100 of length L. Theinitial positions 510 of the seal jaws 51 are thus determined.

If the value of L in the above equation is not known accurately, it canbe ascertained as follows. First, the seal jaws 51 are started fromprovisionally selected starting positions when an eye mark on the film100 is detected. Let t and x respectively denote the time required forthe seal jaws 51 to reach the clamping position 511 and the distancetraveled by the film 100 in the meantime. After the film 100 hastraveled the distance x, it is clamped, sealed and cut to produce a testbag, as shown in FIG. 7. If the position at which the film was cut isdisplaced from the intended cut-position, this displacement e ismeasured and inputted through the input means 40. Corrections on t and xare made according to the following equations by the operating means 22:

T=t±e/V,

X=x±e.

The value of L is obtained therefrom as follows:

L=X−L _(C) 30 nL _(b)

and these corrected values are stored in the memory 21.

The operations described above will be explained next with reference tothe timing chart of FIG. 8. When the user specifies a kind of articlesto be packaged through the input means 40, the corresponding bag sizeand conditions for the operation of the packaging machine are retrievedfrom the memory 21, displayed on a screen of the input means 40 andtransmitted to the operating means 22. The operating means 22 use thesedata to calculate various parameters for the operation of the packagingmachine, including the determination of the initial positions 510 forthe seal jaws 51.

After this preliminary preparation is completed, the user presses astart button (not shown) and causes the computer 20 to transmit startsignals to the control units 85, 54 and 56. The pull-down belts 81 beginto rotate and the film 100 is advanced along its path. The distancetraveled by the film 100 is monitored by the film motion counter 11. Assoon as an eye mark 101 is detected by the eye mark sensor 95, adetection signal is outputted therefrom and the film motion counter 11is thereby reset, starting its counting of pulses from the pulsegenerator 84. At the same time, the seal jaws 51 begin their rotarymotion and reach the clamping position 511 after time T. In themeantime, a cut-position 102 on the film 100 also reaches the clampingposition 511, meeting the seal jaws 51 at the same time, and the film100 is cut there to form a bag.

This cycle of operations is repeated every time one of the eye marks 101is detected by the eye mark sensor 95.

The invention was described above more or less in general terms withreference to only a limited number of embodiments. A few specificexamples of packaging machines will be described next for betterunderstanding of the invention.

A first example of packaging machine according to this invention may becharacterized as being adapted to cause the seal jaws 51 to clamp thefilm 100 after the film 100 is caused to travel a specified distancefrom the moment an eye mark is detected, and the memory 21 stores L_(b),L_(C) and L such that the timing for the clamping by the seal jaws 51 iscontrolled according to the aforementioned specified distance.

A second example of packaging machine may be characterized as beingadapted to cause the seal jaws 51 to clamp the film 100 after the film100 is caused to travel for a specified length of time from the momentan eye mark is detected, and the memory 21 stores not only L_(b), L_(C)and L but also the number N of bags to be produced per unit time. Thespeed of the film 100 is obtained as NL_(b) such that the timing for theclamping by the seal jaws 51 is controlled according to theaforementioned specified length of time.

A third example of packaging machine may be characterized as beingadapted to cause the seal jaws 51 to clamp the film after the film 100is caused to travel under a specified condition (“travel condition”)such as only over a specified distance or for a specified length oftime, and the memory 21 stores for each of various kinds of articles tobe packages corresponding values of N, L_(b) and L_(C), as well as L incommon for all kinds of articles. The input means 40 allows the user tospecify one of these kinds, and data corresponding to the specified kindof articles are similarly retrieved from the memory 21. The operatingmeans 22 uses these data to calculate the aforementioned travelcondition, controlling the timing for the clamping by the seal jaws 51according to this travel condition.

Any of these examples can be further adapted such that the value of Ldefined above can be accurately determined even where its value isinitially not accurately known, as explained above. They can also befurther adapted to adjust the control mode of operation according to aspecified mode of stripping or sealing time.

FIG. 9 shows another control circuit 210 which may be used in thecontrol system shown in FIG. 2 for a packaging machine embodying thisinvention adapted to automatically adjust the position for cutting thefilm 100 merely by transporting the film until the cut-position definedon the film reaches a specified spatial position representing theclamping position, that is, by activating the pull-down belts 81,detecting one of the eye marks 101 while causing the film 100 toadvance, measuring the distance traveled by the film 100 from that pointin time until a cut-position on the film reaches a specified positionand setting the clamping position 511 of the seal jaws 51 on the basisof this measured distance of travel.

Explained more in detail, the control circuit 210 includes a film motioncounter 211, a film motion memory 212, a rotation counter 213, aparameter memory 214, a calculating means 215, a clamping positionmemory 216, and a pattern memory 217 and is provided with an inputdevice 240, as shown in FIG. 9. The film motion counter 211, like thefilm motion counter 11 shown in and explained with reference to FIG. 3above, serves to measure the distance of travel of the film 100 pulledby the pull-down belts 81 in terms of the number of rotation of thebelt-driving motor 83. The film motion memory 212 is for storing thenumber of pulse representing the distance traveled by the film 100 fromwhen one of the eye marks is detected by the eye mark sensor 95 until acut-position marked on the film 100 reaches a specified position such asthe clamping position 511 shown in FIG. 2 where the film 100 traversesthe straight line connecting the axes of rotation of the two arms 52 forthe seal jaws 51. The rotation counter 213 is for measuring the angle ofrotation of the seal jaws 51 from their initial positions 510 until theyreach the clamping position 511 as the number of rotations of thearm-rotating motor 53. The parameter memory 214 is for storing thenumber of pulses representing the angle of rotation of the seal jaws 51from their initial positions 510 to the clamping position 511 for eachpattern of motion. The calculating means 215 is for calculating the timeat which the seal jaws 51 pass their initial positions 510 on the basisof the number of pulses stored in the film motion memory 212. Theclamping position memory 216 is for storing the calculated pulse numberas representing the clamping position for the seal jaws 51. The patternmemory 217 is for controlling the arm-rotating motor 53 and theaxis-shifting motor 55 according to each of different patterns ofmotion. The input device 240 allows the user to specify a pattern ofmotion and transmits a pattern signal to the pattern memory 217accordingly so as to control the operations of the arm-rotating motor 53and the axis-shifting motor 55 through their control units 54 and 56. InFIG. 9, numerals 221 and 222 indicate input keys for starting andstopping the belt-driving motor 83 and the arm-rotating motor 53,respectively.

Next, the operation of the control circuit 210 thus structured will bedescribed with reference to FIGS. 5 and 10A and 10B. After thebelt-driving motor 83 is started by means of the corresponding input key221 to cause the pull-down belt 81 to advance the film 100 (Step S201)and when one of the eye marks 101 is detected by the eye mark detector95 (YES in Step S202), its detection signal activates the film motioncounter 211 and the distance of travel by the film 100 from this pointin time is measured in terms of the number of pulses (Step S203). Thismeasured value is reset and the counting is re-started every time a neweye mark is detected, that is, every time a portion of the film 100corresponding to one bag has been advanced.

Next, when a cut-position defined on the film 100 has passed a specifiedspatial position such as the straight line connecting the axes ofrotations 59 of the two arms 52, that is, when the film 100, movingaccording to a certain pattern of motion, has passed the clampingposition 511 (YES in Step S204), the input key 221 is operated to stopthe motion of the film 100 such that the cut-position on the film willbe at this clamping position 511 (Step S205). At the same time, thepulse number representing the distance by which the film 100 hastraveled thus far is preset in the film motion memory 212 (Step S206) asa reference number. This may be done through an input means which is notshown in FIG. 9. Thus, the distance between the eye mark and thecut-position for each bag is stored.

The angular distance traveled by the seal jaws 51 from their initialpositions 510 until they reach the clamping position 511 ispreliminarily known from the set rate of packaging (or the number ofbags to be produced per unit time) and the initial positions 510. Thisvalue is stored in the parameter memory 214.

Next, the calculating means 215 calculates, on the basis of thereference pulse number inputted as representing the distance traveled bythe film 100, the angle by which the seal jaws 51 have rotated from whenthe eye mark was detected until they reach the clamping position 511,determining therefrom the timing of the seal jaws 51 for starting tomove from their initial positions 510 (Step S207). If the number ofpulses corresponding to the distance from one eye mark to the next is1000 and that corresponding to the distance between one eye mark to thenext cut-position is 500, this means that the seal jaws 51 must be abouta half rotation before reaching the clamping position 511 when the eyemark is detected because the seal jaws 51 must make a complete rotationwhile the film 100 travels a distance corresponding to 1000 pulses. Onthe other hand, the angle of rotation (as well as the time interval)from when the seal jaws 51 leave their initial positions 510 until theyreach the clamping position 511 is stored in the parameter memory 214.If the number of pulses corresponding to this angle (or the timeinterval) is 300, for example, the seal jaws 51 should be started fromtheir initial positions 510 after the time corresponding to (500−300=)200 pulses has elapsed such that they will reach the clamping position511 after a time interval corresponding to 300 pulses and thecut-position on the film 100 will also reach the clamping position 511at the same time.

The timing for starting the motion of the seal jaws 51 is thusdetermined and stored in the clamping position memory 216 (Step S208).If the motion of the seal jaws 51 is thus started according to thistiming after the eye mark is detected, they match exactly with thecut-position on the film 100 at the clamping position 511.

If the packaging speed is changed, if the stripping distance is adjustedaccording to the kind of articles to be packaged, or if the sealing timeis altered according, say, to the kind of film being used, that is, ifcontrol parameters of the operations are changed, the patterns of motionof the arm-rotating and axis-shifting motors 53 and 55 must also bechanged because not only the angular speed of the seal jaws 51 betweenthe initial positions 510 and the clamping position 511 but also theclamping position 511 itself will change.

To understand this situation more clearly, FIG. 5 may be referenced onceagain. As shown in FIG. 5 and explained above with reference thereto,the seal jaw trajectory is generally divided into an accelerating partW_(a), a preparatory part W_(b), a stripping part W_(c), a sealing partW_(d), a transition part W_(e) and a return part W_(f). As explainedabove with reference to FIGS. 3 and 4, the clamping position 511 willshift if the stripping distance (indicated above by symbol D₁) and/orthe sealing time is changed, and the contents of the parameter memory214 change accordingly.

Thus, if a change in the packaging speed or other conditions ofoperation such as the stripping distance or the sealing time isspecified through the input device 240 (YES in Step S209 of FIG. 10B),the pattern memory 217 responds by outputting pulse signals indicativeof a new angular speed of the seal jaws 51 and a new clamping position,controlling the rotary motions of the arm-rotating and axis-shiftingmotors 53 and 55 accordingly (Step S210). Thereafter, the angulardistance and the timing between the initial positions 510 and theclamping position 511 for the seal jaws 51 are calculated (Step S211)and stored (Step 212). The timing for the starting of motion from theinitial positions 510 is likewise calculated, as explained above, fromthe distance traveled by the film 100, and this is stored in theclamping position memory 216 such that the film 100 can be cut exactlyat the desired cut-position.

In summary, many modifications and variations are possible on thedescribed embodiments and examples. Such modifications and variationsthat are apparent to a person skilled in the art are intended to bewithin the scope of this invention.

What is claimed is:
 1. A cut-position adjusting device for a packagingmachine, said packaging machine comprising means for causing anelongated film having detectable eye marks thereon to travel on a path,a pair of seal jaws for moving cyclically to clamp and cut the filmtransversely to form a separated bag and a detector for detecting theeye marks, said device comprising; a memory for storing a condition forcausing said seal jaws to start moving after one of said eye marks isdetected by said detector as said film travels on said path; input meansfor allowing a user to input a displacement value according to whichsaid condition is to be changed, said displacement value representing ameasured distance between a test cut position at which a dummy bag iscut by said packaging machine in a test and a desired cut position atwhich said dummy bag was aimed to be cut; and control means foradjusting said condition according to said displacement value inputtedthrough said input means so as to eliminate said displacement value.